The present invention relates to photosensitive chips for creating electrical signals from an original image, as would be found, for example, in a digital scanner, copier, facsimile machine, or other document generating or reproducing device.
Image sensor arrays typically comprise a photosensitive array of photosites which raster scan an image bearing document and convert the microscopic image areas viewed by each photosite to image signal charges. Each photosite includes one or more photodiodes, photogates or other photodetection devices. Following an integration period, the image signal charges are amplified and transferred as an analog video signal to a common output line or bus through successively actuated multiplexing transistors.
For high-performance image sensor arrays, a preferred design includes a photosensitive array of photosites of a width comparable to the width of a page being scanned, to permit one-to-one imaging generally without the use of reductive optics as taught in U.S. Pat. No. 5,473,513. In order to provide such a xe2x80x9cfull-widthxe2x80x9d array, however, relatively large silicon structures must be used to define the large number of photosites as shown in FIG. 1. A preferred technique to create such a large array is to assemble several photosensitive chips 101 through 10N end to end on a base substrate 20, each chip 10 defining a small photosensitive array thereon. The base substrate 20 is preferably a form of ceramic such as alumina, and the chips 10 are preferably made of silicon or another semiconductor material. N is defined as any whole number.
Alternatively, chip 10 may represent a charged-coupled device (CCD) or another type of photosensitive semiconductor chip.
The chips 10, which are assembled end to end to form one full-width array, are created by first creating the circuitry for a plurality of individual chips 10 on a single silicon wafer. The silicon wafer is then cut, or xe2x80x9cdiced,xe2x80x9d around the circuit areas to yield discrete chips 10. Typically, the technique for dicing the chips 10 includes a combination of chemical etching and mechanical sawing. Because, on each chip 10, the photosites are spaced with high resolution from one end of a chip 10 to the other, the cutting of the chips 10 from the wafer requires precision dicing. It would be desirable to dice each individual chip 10 with a precise dimension along the photosensitive array of photosites, so that, when a series of chips 10 are assembled end-to-end to form a single page-width photosensitive array, there is a minimum disruption of spacing from an end photosite on one chip 10 to a neighboring photosite at the end of a neighboring chip 10. Typically, there is a small gap 30 between two adjacent chips 10. Ideally, the geometric centers of the photosites should be collinear and the photosites should be uniformly spaced across an entire full-width photosensitive array regardless of the configuration of silicon chips 10 forming the photosensitive array. In the prior art, photosites in the chips 10 were made in a square or rectangular shape to provide a repetitive structure of photosites 40. In this way, the repetitive structure was maintained on a chip-to-chip basis, particularly in the gaps 30 between adjacent chips 10 as shown in FIG. 2.
As shown in FIG. 2, the photosites 40 typically have a rectangular shape, wherein each photosite 40 is smaller in the x-direction (fast scan direction) than the y-direction (slow scan direction or direction of document motion) to allow for electrical isolation, to limit cross talk and to allow for conductive traces to run between photosites. As a result, the optical modulation transfer function (MTF) of the system is higher in the x-direction (fast scan direction) than in the y-direction (slow scan direction). The fact that the document to be scanned moves in the y-direction further reduces the y-MTF. However, the negative consequences of the high x-MTF need to be addressed.
For example, half-tone documents typically have a certain dot frequency in the x-direction. Since a beat occurs between the dot frequency and the frequency of the photosite locations, undesirable Moirxc3xa9 patterns appear on the reproduced documents. Therefore, there is a need for a new photosensitive array of photosites, which reduces or eliminates the Moirxc3xa9 patterns particularly in the x-direction (fast scan direction).
As shown in FIG. 3, there were attempts in the prior art to improve image quality at the boundary of adjacent chips by providing photosites having two different shapes on photosensitive chips. This pattern was generally disclosed in U.S. Pat. No. 5,552,828. The regular photosites 60 have a generally square shape or slightly rectangular shape whereas the end photosites 70 have a trapezoidal shape. The advantage of the generally trapezoidal shape of end photosites 70 is that, while the overall width of each end photosite 70 is equal to that of each regular photosites 60, the geometric center of the end photosites 70 is made slightly closer to the edge of the chip 10 to help compensate for any chip spacing problems between the chips 10. However, this arrangement of shapes does not reduce or eliminate Moirxc3xa9 patterns.
U.S. Pat. No. 5,031,032 discloses a pattern of photosites for a full width photosensitive array with photosites of different colors. Although multiple geometric shapes are used to form a rectangular photosite with the three different primary colors, this arrangement of shapes does not reduce or eliminate Moirxc3xa9 patterns.
According to the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of complementary shaped photosites on a chip, wherein the largest dimension of at least one photosite on a chip in the fast scan direction is longer than a pitch between two adjacent photosites in the fast scan direction. Preferably, the largest dimension of each photosite on a chip in the fast scan direction is longer than a pitch between two adjacent photosites. The photosensitive array may be a linear array or a two dimensional array. The array preferably extends from one end of the chip to the other, and the array of complementary shaped photosites is preferably buttable. The array can be used in single chip applications. However, the complementary shaped photosites on a chip are preferably adapted for end to end assembly with like arrays on like chips to form a full width array.
According to the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of complementary triangular, trapezoidal or pentagonal shaped photosites on a chip extending from one end of the chip to the other. The photosensitive array reduces the modulation transfer function in the fast scan direction to reduce Moirxc3xa9 patterns. Each photosite has a photodetection device such as a photodiode or photogate and each photosite has the same surface area. A photosensitive array can be mounted on a substrate adjacent to a second photosensitive array of complementary shaped photosites wherein the last shape of the photosensitive array and the first shape of the second photosensitive array are complementary. A plurality of the photosensitive arrays can be juxtaposed and mounted on a rectangular substrate to form a full width photosensitive array. In several embodiments, the photosensitive arrays on the chips are buttable. The photosensitive array may be a linear array or two dimensional array. Further, the photosensitive array may be used independently to scan an image or can be juxtaposed with one or more photosensitive arrays to scan an image.
According to the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of interlocking photosites on a chip extending from one end of the chip to the other. The photosensitive array reduces the modulation transfer function in the fast scan direction to reduce Moirxc3xa9 patterns. Each interlocking photosite has a photodetection device such as a photodiode or photogate and each photosite has the same surface area. A photosensitive array can be mounted on a substrate adjacent to a second photosensitive array, wherein the last interlocking photosite of the photosensitive array and the first interlocking photosite of the second photosensitive array have an outer edge, which is parallel to the chip edge. A plurality of the photosensitive arrays can be juxtaposed and mounted on a rectangular substrate to form a full width photosensitive array. The photosensitive arrays on the chips are buttable. Further, one photosensitive array may be used to scan an image or can be juxtaposed with one or more photosensitive arrays to scan an image. The photosensitive array may be a linear array or two dimensional array. The largest dimension of at least one photosite in the fast scan direction is longer than the pitch between adjacent photosites in the fast scan direction. Preferably, the largest dimension of each photosite in the fast scan direction is longer than the pitch between adjacent photosites.
According to another embodiment of the present invention, there is provided a photosensitive array having a fast scan direction and a slow scan direction, wherein the photosensitive array includes an array of photosites on the chip extending from one end of the chip to the other including slanted photosites and an end photosite, the slanted photosites being generally in the shape of a parallelogram without right angles, the end photosite being generally in the shape of a trapezoid having a first edge, a second edge, an inner edge facing the slanted photosites and an outer edge facing the chip end, wherein the outer edge forms two 90 degree angles with the first and second edges. Preferably, the outer edge is shorter than the inner edge. Each photosite has a photodetection device such as a photodiode or photogate, and each photosite has the same surface area. In addition, the photosites are collinear. A photosensitive array can be mounted on a substrate adjacent to a second photosensitive array. A plurality of the photosensitive arrays can be juxtaposed and mounted on a rectangular substrate in an end to end relationship and extending from one end of the substrate to the other to form a full width photosensitive array. Further, one photosensitive array may be used to scan an image or can be juxtaposed with one or more photosensitive arrays to scan an image. The photosensitive array may be a linear array or two dimensional array. The largest dimension of at least one photosite in the fast scan direction is longer than the pitch between adjacent photosites in the fast scan direction. Preferably, the largest dimension of each photosite in the fast scan direction is longer than the pitch between adjacent photosites.
According to another embodiment, there is provided a digital copier including a raster scanner scanning documents to generate digital image signals; a controller directing a raster output scanner to expose a photoconductive belt, to create an electrostatic latent image based on image signals received from the raster input scanner; a developer applying toner to the latent image; a transfer station transferring the toner of the latent image to a sheet of paper; and a fuser permanently affixing the toner to the sheet of paper. A raster input scanner includes a plurality of chips, which are juxtaposed and mounted on a substrate forming an array of complementary shaped photosites, wherein the complimentary shaped photosites consist of trapezoids, triangles and pentagons. The trapezoidal shaped photosites and pentagonal shaped photosites can be buttable. Each complementary shape has a photodetection device. Each complementary shape has the same surface area. The pentagonal shaped photosites are collinear. The photosensitive array may be a linear array or two dimensional array.
Alternatively, the raster input scanner includes a plurality of chips, which are juxtaposed and mounted on a substrate forming an array of interlocking photosites. The last interlocking photosite of the photosensitive array and the first interlocking photosite of the second photosensitive array have an outer edge, which is parallel to the chip edge. Therefore, the photosensitive arrays are buttable. Each complementary shape has the same surface area, and the interlocking photosites are collinear. The photosensitive array may be a linear array or two dimensional array.
Alternatively, the raster scanner includes a plurality of generally rectangular chips, which are juxtaposed and mounted on a substrate forming an array of photosites including slanted photosites and an end photosite, the slanted photosites being generally in the shape of a parallelogram without right angles, the end photosite being generally in the shape of a trapezoid having a first edge, a second edge, an inner edge facing the slanted photosites and an outer edge facing the chip end. The outer edge forms two 90 degree angles with the first and second edges. Each photosite has a photodetection device, and each photosite has the same surface area. The photosites are collinear. The photosensitive array may be a linear array or two dimensional array.